Mark Zuckerberg

Net Worth: $9.4 billion
Mark Zuckerberg, cofounder and chief executive officer at Facebook, saw his fortune fall $8.1 billion following the precipitous drop of shares in the Menlo Park, Calif. social networking giant. Since Facebook debuted on the Nasdaq at $38 a share in May, the stock price has dipped below $20, dropping more than 48% as of late August. The decline isn't likely to change the hoodie-wearing CEO's lifestyle much. What's less clear: whether the 28-year-old executive, who married his longtime girlfriend Priscilla Chan the day after the IPO and headed off for an Italian honeymoon, can right the ship and make Facebook into a winning public company. Speaking at a TechCrunch conference in September, Zuckerberg noted, "I personally would rather be underestimated."